Vim: substitute support (#2641)

Release Notes:

- vim mode now supports `s` for substitute

crates/vim/src/normal/substitute.rs

@@ -0,0 +1,69 @@
+use gpui::WindowContext;
+use language::Point;
+
+use crate::{motion::Motion, Mode, Vim};
+
+pub fn substitute(vim: &mut Vim, count: usize, cx: &mut WindowContext) {
+    vim.update_active_editor(cx, |editor, cx| {
+        editor.set_clip_at_line_ends(false, cx);
+        editor.change_selections(None, cx, |s| {
+            s.move_with(|map, selection| {
+                if selection.start == selection.end {
+                    Motion::Right.expand_selection(map, selection, count, true);
+                }
+            })
+        });
+        editor.transact(cx, |editor, cx| {
+            let selections = editor.selections.all::<Point>(cx);
+            for selection in selections.into_iter().rev() {
+                editor.buffer().update(cx, |buffer, cx| {
+                    buffer.edit([(selection.start..selection.end, "")], None, cx)
+                })
+            }
+        });
+        editor.set_clip_at_line_ends(true, cx);
+    });
+    vim.switch_mode(Mode::Insert, true, cx)
+}
+
+#[cfg(test)]
+mod test {
+    use crate::{state::Mode, test::VimTestContext};
+    use indoc::indoc;
+
+    #[gpui::test]
+    async fn test_substitute(cx: &mut gpui::TestAppContext) {
+        let mut cx = VimTestContext::new(cx, true).await;
+
+        // supports a single cursor
+        cx.set_state(indoc! {"ˇabc\n"}, Mode::Normal);
+        cx.simulate_keystrokes(["s", "x"]);
+        cx.assert_editor_state("xˇbc\n");
+
+        // supports a selection
+        cx.set_state(indoc! {"a«bcˇ»\n"}, Mode::Visual { line: false });
+        cx.assert_editor_state("a«bcˇ»\n");
+        cx.simulate_keystrokes(["s", "x"]);
+        cx.assert_editor_state("axˇ\n");
+
+        // supports counts
+        cx.set_state(indoc! {"ˇabc\n"}, Mode::Normal);
+        cx.simulate_keystrokes(["2", "s", "x"]);
+        cx.assert_editor_state("xˇc\n");
+
+        // supports multiple cursors
+        cx.set_state(indoc! {"a«bcˇ»deˇffg\n"}, Mode::Normal);
+        cx.simulate_keystrokes(["2", "s", "x"]);
+        cx.assert_editor_state("axˇdexˇg\n");
+
+        // does not read beyond end of line
+        cx.set_state(indoc! {"ˇabc\n"}, Mode::Normal);
+        cx.simulate_keystrokes(["5", "s", "x"]);
+        cx.assert_editor_state("xˇ\n");
+
+        // it handles multibyte characters
+        cx.set_state(indoc! {"ˇcàfé\n"}, Mode::Normal);
+        cx.simulate_keystrokes(["4", "s", "x"]);
+        cx.assert_editor_state("xˇ\n");
+    }
+}